I thought this was a pretty good list. I am a user of linkedin. It is interesting to see that search is a item on the list you would think between google and yahoo it would be a dead end. Also, the technology around mobile is just starting to pick up. Advertising, search, useablity are all items that are being used on mobile devices
http://www.wired.com/techbiz/startups/news/2007/12/YE_10_startups